As a type of cutting tool used in, for example, turning, inserts including TiCN-based cermet (hereinafter to be simply referred to as cutting inserts) are known in the prior art.
Known examples of the aforementioned cutting inserts have the compositions shown below.
(a) TiCN-based cermet in the form of a sintered body of a compact having a blended composition including in percent by mass (hereinafter “%” refers to “mass %) of:
tungsten carbide (hereinafter referred to as WC): 20 to 30%;
one kind or two kinds of tantalum carbide (hereinafter referred to as TaC) and niobium carbide (hereinafter referred to as NbC) (hereinafter referred to as TaC/NbC): 5 to 10%;
Co: 5 to 10%;
Ni: 5 to 10%; and
titanium carbonitride (hereinafter referred to as TiCN): 50 to 60%.
(b) The aforementioned TiCN-based cermet has a microstructure including
hard phase: 75 to 90 area %, and
binding phase: balance. Here, the surface area ratio is the value measured by observing the microstructure with a scanning electron microscope.
The aforementioned hard phase contains the following (1) to (3) as indicated in the schematic drawing of FIG. 2 showing the results of observing microstructure with a scanning electron microscope (magnification: 10,000-fold).
(1) First hard phase having a core-having structure in which a core portion includes a TiCN phase and a peripheral portion includes a complex carbonitride of Ti, W and one or both of Ta and Nb (hereinafter indicated as (Ti,W,Ta/Nb)CN);
(2) Second hard phase having a core-having structure in which both a core portion and a peripheral portion include (Ti,W,Ta/Nb)CN phases; and
(3) Third hard phase having a single phase structure including a TiCN phase.
The aforementioned binding phase includes a Co—Ni alloy having a composition containing, as the ratio in the binding phase and by mass %,
W: 1 to 10%,
Ni: 35 to 60%,
Ti and one kind or two kinds of Ta and Nb (to be indicated as Ta/Nb), the total amount thereof being 5% or less, and
Co as the balance.
In addition, the following indicates known examples of cutting inserts containing one kind or two or more kinds of zirconium carbide (hereinafter referred to as ZrC), vanadium carbide (hereinafter referred to as VC) and molybdenum carbide (hereinafter referred to as Mo2C) (hereinafter referred to as ZrC/VC/Mo2C)
(a) TiCN-based cermet in the form of a sintered body of a compact having a blended composition including: in percent by mass (hereinafter “%” refers to “mass %”)
WC: 20 to 30%;
TaC/NbC: 5 to 10%;
ZrC/VC/Mo2C: 1 to 5%;
Co: 5 to 10%;
Ni: 5 to 10%; and
TiCN: 50 to 60%.
(b) The aforementioned TiCN-based cermet has a microstructure including
hard phase: 75 to 93 area %, and
binding phase: balance. Here, the surface area ratio is the value measured by observing the microstructure with a scanning electron microscope.
The aforementioned hard phase contains the following (1) to (3) as indicated in the schematic drawing of FIG. 3 showing the results of observing microstructure with a scanning electron microscope (magnification: 10,000-fold).
(1) First hard phase having a core-having structure in which a core portion includes a TiCN phase and a peripheral portion includes a complex carbonitride of Ti, W, one kind or two kinds of Ta and Nb, and one kind or two or more kinds of Zr, V and Mo (hereinafter indicated as (Ti,W,Ta/Nb,Zr/V/Mo)CN);
(2) Second hard phase having a core-having structure in which both a core portion and a peripheral portion include (Ti,W,Ta/Nb,Zr/V/Mo)CN phases; and
(3) Third hard phase having a single phase structure including a TiCN phase.
The aforementioned binding phase includes a Co—Ni alloy having a composition containing: as the ratio in the binding phase and by mass %,
W: 1 to 10%;
Ni: 35 to 60%;
Ti, one kind or two kinds of Ta and Nb (to be indicated as Ta/Nb), and one kind or two or more kinds of Zr, V and Mo (to be indicated as Zr/V/Mo), the total amount thereof being 5% or less; and
Co as the balance.
Moreover, a cutting insert as described above is commonly known to be produced by sintering a compact having the aforementioned blended composition under conditions consisting of the steps of the following sintering conditions (i) to (iii), and is used for continuous cutting and intermittent cutting of various types of steels and cast irons.
(i) The temperature is raised from room temperature to 1400 to 1450° C. in a vacuum atmosphere of 10 Pa or less at the rate of 1 to 3° C./min.
(ii) The temperature is raised from 1400 to 1450° C. to a sintering temperature of 1480 to 1560° C. at the rate of 1 to 3° C./min and then holding for 0.5 to 2 hours at the aforementioned sintering temperature. This raising of the temperature and holding at the predetermined temperature are carried out in a nitrogen atmosphere of 50 to 4000 kPa.
(iii) The furnace is cooled from the aforementioned sintering temperature in a vacuum atmosphere of 10 Pa or less.
The performance of cutting apparatuses has increased dramatically in recent years, while demands being placed on cutting with respect to conservation of power, conservation of energy and reduction of costs have become increasingly severe. Accompanying these demands, cutting speeds are tending to increase. However, in the case of cutting steel or cast iron and the like at high cutting speeds of 300 m/min or more using a conventional cutting insert as described above, wear of the binding phase composed of Co—Ni-based alloy of TiCN-based cermet that composes these cutting inserts in particular is accelerated considerably. This causes the current comparatively short service life of these cutting inserts.
In addition, cermet inserts having a microstructure composed of hard phases (hard particles) and binding phase present between the hard phases are used to cut steel and the like, and various technologies have been proposed for improving the performance of these cermet inserts.
For example, Patent Document 2 proposes a TiCN-based cermet composed of an ordinary core-having structure, and more specifically, a core-having structure composed of a plurality of phases consisting of a phase in which a core portion is rich in a group 4a element such as Ti and a peripheral portion is rich in group 5a and group 6a elements such as W and Ta (black phase), and a phase in which a core portion is rich in group 5a and group 6a elements such as W and Ta (white phase), wherein strength of cermet alloy is improved by dispersing the black phase and the white phase at the optimum ratio.
However, in the technology proposed by the aforementioned Patent Document 2, although strength of cermet alloy is improved to a certain degree according to the composition of the black phase and white phase as described above, it has the problem of adequate considerations not necessarily being given to wear resistance and breakage resistance.
(Patent Document 1) Japanese Unexamined Patent Application, First Publication No. H10-110234
(Patent Document 2) Japanese Unexamined Patent Application, First Publication No. S62-170452